An ultrasonic receiver can be used to determine the location of items that contain ultrasonic emitters, such as a mobile device present within a retail, factory, or warehouse environment, for example. The ultrasonic emitter can transmit ultrasonic energy in a short burst which can be received by an ultrasonic transducer (microphone) in the ultrasonic receiver, thereby establishing the presence of the device within the environment.
Further, the use of several ultrasonic receivers distributed within the environment can also be used to provide a specific location of a particular device using techniques known in the art such as triangulation, trilateration, and the like. However, unlike radio frequency locationing systems, ultrasonic locationing systems suffer from particular problems related to the character of ultrasonic sound waves and their environment of use. Firstly, ultrasonic waves are typically subject to acoustic reverberation. Therefore, a first signal sent by a first emitter directly followed by a second signal sent by a second emitter may cause the second signal to be missed by the receiver, due to the second signal arriving at the receiver during the reverberation of the first signal. Secondly, ultrasonic signals are vastly slower than radio frequency signals. Therefore, a first signal sent by a first emitter followed by a second signal sent by a second emitter could arrive at the receiver simultaneously preventing reception by the receiver, due to the second emitter being closer to the receiver.
The obvious solution to this problem is to provide a time buffer in the system such that a signal sent by any emitter in the system will be properly received by the receiver before any other emitter in the system can send a signal to the receiver. This solution entails determining a maximum flight time for a signal from any emitter within the reading environment, and also determining a time for reverberations to die down before any other signal can be received. These two times are added to provide a buffer time period. The system then guarantees that any emitter can only emit an ultrasonic signal at least one buffer time period after any another other emitter can send an ultrasonic signal to the receiver.
However, due to the relatively long reverberation and flight times of ultrasonic sound waves, the use of a buffer time period will not produce signal repetitions to refresh a device position at a high enough rate when there are many emitters in the system.
Accordingly, there is a need for an improved technique to resolve the above issues with an ultrasonic positioning system.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.